The present invention relates to semiconductor integrated circuits with voltage-detecting circuits, and signal transmitting and receiving systems.
The following describes a conventional method of recognizing connection between semiconductor integrated circuits having an interface, such as in an IEEE 1394 standard interface, with which the semiconductor integrated circuits are connected to each other by cables.
A semiconductor integrated circuit (hereafter referred to as “LSI”) has, its inside, a voltage-generating circuit for supplying a predetermined voltage to a cable connected thereto, a cable voltage-detecting circuit for detecting the voltage of the connected cable, and a power supply voltage-detecting circuit for detecting a power supply voltage to stop the supply of the predetermined voltage from the voltage-generating circuit to the cable when the power supply voltage becomes lower than a set voltage. The following describes recognition of the connection state in which two LSIs, LSI 1 and LSI 2 each having the foregoing voltage-generating circuit, the cable voltage-detecting circuit, and, the power supply voltage-detecting circuit, are connected to each other by two cables.
The LSI 1 supplies a predetermined voltage from the voltage-generating circuit to a first cable. The voltage is detected by the cable voltage-detecting circuit in the LSI 2 and it is recognized that the LSI 2 is connected with the LSI 1. Meanwhile, the LSI 2 also supplies a predetermined voltage from the voltage-generating circuit to a second cable; the LSI 1 detects the voltage with the cable voltage-detecting circuit and it is recognized that the LSI 1 is connected with the LSI 2. The voltage-generating circuit in each of the LSIs continues to supply the predetermined voltage to the first and the second cables respectively until the interconnection therebetween is cut off.
In such a state of connection, for example, when the power supply of the LSI 1, one of the LSIs, is completely shut off and the power supply voltage becomes lower than a set voltage, the power supply voltage-detecting circuit detects the voltage decrease and the supply of the predetermined voltage from voltage-generating circuit to the first cable is cut off. Accordingly, the voltage of the first cable decreases lower than a predetermined voltage, the cable voltage-detecting circuit in the LSI 2, the other one of the LSIs, detects the voltage decrease and recognizes that the LSI 1 is disconnected. Thereafter, when power is again turned on for the LSI 1, a predetermined voltage is supplied from the voltage-generating circuit therein to the first cable, and the cable voltage-detecting circuit in the LSI 2, which is the other LSI, re-recognizes that the LSI 1 is connected.
The above-described conventional configuration has at least the following drawback. If the voltage detection level for the power supply is set low, the operation of the power supply voltage-detecting circuit becomes unstable. On the other hand, if the voltage detection level is set high, the power supply voltage-detecting circuit starts to operate when the power supply voltage is made lower than the voltage detection level to evaluate an operation of the LSI, and consequently the voltage-generating circuit stops the operation. For this reason, it is very difficult to set the voltage detection level of the power supply voltage-detecting circuit.
Moreover, in the foregoing conventional configuration, in cases where the power supply voltage suddenly drops during the shut-off of the power supply, the duration in which a voltage-detected signal is output from the power supply voltage-detecting circuit is extremely short, and therefore, the voltage-generating circuit does not properly operate in such a short duration. For this reason, the voltage of the first cable does not decrease to a voltage that is lower than a connection detection level. As a result, although the power supply has been shut off, the second LSI 2 can misrecognize that the first LSI 1 is still connected.